This invention generally relates to the manufacture of semiconductor substrates, particularly for use in the electronics, optoelectronics or optics industry.
Substrates composed of a film or thin layer on a thicker support are known. Electronic, optoelectronic or optical components are fabricated in the thin film or useful layer of such a substrate. During manufacturing, the thin film is separated from the support and if necessary applied onto another support. Techniques have recently been developed for separating a useful thin layer from its support.
The “epitaxial lift off” technique is well known in the domain of elements in the Group III-V classification, and consists of inserting a second thin layer between a support and a thin layer. The second thin layer is called a sacrificial layer, and this sacrificial layer is epitaxially grown. A first epitaxy operation is used to fabricate the sacrificial layer on the support, and the useful thin layer is also made by epitaxy. The sacrificial layer is made so that it can be selectively etched with respect to the support and the useful thin layer. For example, an AlAs sacrificial layer is formed between a GaAs support and a useful layer of AlGaAs. In this known technique, the sacrificial layer obtained by using a hetero-epitaxy process is monocrystalline and is thin. Its nature depends on the support material upon which growth takes place.
The epitaxial lift off technique has been described in an article called: “Ultra-high efficiency light-emitting diodes through epitaxial lift-off packaging” by M. Sickmiller et al., International Symposium on Microelectronics, 1998. Its usefulness has been demonstrated for support surfaces and thin layers with an area on the order of a few square centimeters. However, further tests have cast doubt on the feasibility of this technique for significantly larger areas, for example, areas on the order of a few hundred cm2 which are used in industrial substrates.
Another solution for making a separable bond consists of forming a molecular bond between a support and a thin layer, and then separating at the bonding interface at the opportune time. Bond forces obtained during this type of bonding vary depending on different parameters (such as the roughness of the surfaces, the hydrophilic properties of surfaces, the chemical affinity between materials, their tendency to creep, the temperature, and the like). In some cases, forming a separable bond in this manner could be considered. However, after using this type of bonding technique, if the thermal budget applied to the thin layer is large, then the bonding interface will be reinforced and separation will become more difficult, if not impossible.
During the manufacture of substrates for LEDs, the temperatures of some treatments (particularly epitaxy using the MOCVD technique) can reach or significantly exceed 1000 to 1100° C. In particular, when manufacturing substrates for LEDs, it may be necessary to carry out heat treatments on the support and thin film assembly using such high temperatures. For example, thermal oxidation steps or surface smoothing steps under a hydrogenated atmosphere may be required to prepare the surface before nitrides or other elements are deposited by epitaxy. These steps can occur at temperatures of more than 1150° C. If a molecular bond has been formed between two oxide layers, for example, that were added onto a support and a thin layer made of silicon carbide SiC, such temperatures would considerably increase the bonding forces causing them to reach a value of at least 2 Joules/m2. Such a high bonding force makes separation impossible. It would thus be beneficial to provide a separable bonding interface, particularly for manufacturing substrates for LEDs such as blue, green or ultraviolet (UV) LEDs, which maintains separable properties even after treatment at high temperatures (in the range of about 1100° C. to about 1150° C. or more).